This invention relates to a corrosion-resistant clad end plate for a pressure vessel subject to high pressure, and more particularly to an end plate which is high in corrosion resistance, is highly stable and is clear of the possibility of thickness reduction and peeling of clad members.
Generally speaking, in the case of a urea synthesizing tower, ethanol synthesizing equipment or the like which is subject to high pressure, the corrosion of end plate portions of a spherical shell at its top and bottom ends is serious, and loose lining and other techniques are not applicable. During operation, a gap develops between the pressure-resistant member forming an outer shell and the inner corrosion-resistant lining so that the lining is elongated by internal pressure to the extent corresponding to the gap, and a large stress is thus generated in the lining. This occurs, because the internal temperature of the vessel is high and the coefficient of thermal expansion of the liner of titanium or the like is smaller than that of the pressure-resistant member.
Furthermore, since the liner is cooled quickly whereas the pressure-resistant member is cooled slowly during shutdown, the gap between them becomes larger so that the internal pressure is exerted mainly on the liner and, hence, the stress on the liner becomes quite high. Loose lining is thus difficult to use from the viewpoint of strength.
One way to secure adequate corrosion resistance for the end plates of a pressure-resistant vessel is to join corrosion-resistant members (1) of a thickness suitable for withstanding internal pressure to form an end plate by one-piece molding or welding as seen in FIG. 1. An alternative way is to clad corrosion-resistant cladding members (3) to pressure-resistant base members (2) of a suitable thickness for withstanding internal pressure, cut off the cladding members (3) by a predetermined spacing at each of joints, insert dead members (4) into the spaces left by the cut-off portions and cover the dead members with patches (5) welded to the cladding members (3), thus completely covering the interior of the vessel with corrosion-resistant material. The former of the above two measures is uneconomical because of the use of thick plates of expensive corrosion-resistant material. For the latter, the plate-like cladding members should be shaped into a spherical shell by hot pressing, and annealing should be carried out on the welded portions of the cladding base members to remove welding stresses if this was not done not only would the cladding members thermally deteriorate and lose corrosion resistance during hot forming but the adhesive strength of the clads would decline, resulting in peeling or thickness reduction of the cladding members.